1. Field of the Invention
The present invention is related to a microphone unit, and a sound input apparatus.
2. Description of the Related Art
When telephone communications established by telephones, speech recognition, sound recording operations, and the like are carried out, it is desirable to collect only target voices (voices of users). However, under use environments of voice input apparatuses, sounds other than target voices such as background noise may be present. As a result, voice input apparatuses having functions capable of eliminating noises have been actively developed, by which voices of users can be correctly extracted even in such a case that these voice input apparatuses are utilized under such an environment that noises are present.
As technical ideas capable of eliminating noises under use environments where these noises are present, methods for eliminating noises by applying sharp directivity to microphone units have been proposed in the technical field. Otherwise, other methods for eliminating noises by performing such a signal processing operation that incoming directions of sound waves are discriminated by utilizing incoming time differences of the sound waves. The above technical ideas are disclosed in JP-A-7-312638, JP-A-9-331377 and JP-A-2001-186241.
Also, in recent year, compactnesses of electronic appliances have been progressed, so that such technical ideas capable of making voice input apparatuses compact may constitute important factors.
In order to give sharp directivity to microphone units, a large number of vibration films must be arranged. As a result, it is difficult to make these voice input apparatuses compact.
Also, in order to detect incoming directions of sound waves in higher precision by utilizing incoming differences of the sound waves, a plurality of vibration films must be arranged in such an interval nearly equal to 1/several wavelengths of audible sound waves. As a result, the voice input apparatuses can be hardly made compact.
Moreover, under such an environment that there is substantially no noise, it is not necessarily required to actively remove noises. Conversely, it is desirable to improve SNRs (Signal-to-Noise Ratios) with respect to noises generated in microphone units.